The influence of spreading rate, basement composition, fluid chemistry and chimney morphology on the formation of gold-rich SMS deposits at slow and ultraslow mid-ocean ridges
The influence of spreading rate, basement composition, fluid chemistry and chimney morphology on the formation of gold-rich SMS deposits at slow and ultraslow mid-ocean ridges
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扩散速率、基底成分、流体化学和烟囱形态对慢速和超慢速洋中脊富金 SMS 矿床形成的影响
DOI：
10.1007/s00126-017-0762-4
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发表时间：
2017
影响因子：
4.8
通讯作者：
D. Knight R
中科院分区：
文献类型：
--
作者：
D. Knight R
海底块状硫化物(SMS)矿床富含贵金属，包括黄金。然而，用来解释含金矿床形成的过程通常不适用于大洋中脊环境。在这里，我们表明，在非沉积的大洋中脊，SMS矿床的平均金矿浓度与扩张速度之间存在统计上的显著负相关。位于缓慢扩张脊(20-40 mm/a)的矿床的平均金含量在850-1600 ppb之间；然而，随着扩张速度的增加(高达140 mm/a)，金的浓度逐渐下降到~50-150 ppb之间。金含量与扩散速率的这种相关性可能受流体-岩石相互作用的程度和持续时间的控制，而流体-岩石相互作用的程度和持续时间是热通量、地壳结构(断裂作用)和源岩渗透率的函数。超低山脊的矿床，包括超镁铁质矿床，特别富含黄金。这归因于通过蛇纹岩作用获得的超镁铁质源岩具有较高的渗透率和蛇纹石矿物的固有孔隙度，再加上橄榄岩中的金含量比大洋中脊玄武岩相对较高。流体化学的变化，如还原条件和超镁铁质赋存地点硫有效性增加的可能性，也可能是造成观察到的高浓度的原因。蜂窝烟囱为金的沉淀提供了更有利的条件，由于扩散的低速喷口比玄武岩喷口更集中的喷口，蜂窝烟囱在超镁铁质矿点可能更普遍。
Seafloor massive sulphide (SMS) deposits are variably enriched in precious metals including gold. However, the processes invoked to explain the formation of auriferous deposits do not typically apply to mid-ocean ridge settings. Here, we show a statistically significant, negative correlation between the average gold concentration of SMS deposits with spreading rate, at non-sedimented mid-ocean ridges. Deposits located at slow spreading ridges (20–40 mm/a) have average gold concentrations of between 850 and 1600 ppb; however, with increasing spreading rate (up to 140 mm/a), gold concentrations gradually decrease to between ~ 50 and 150 ppb. This correlation of gold content with spreading rate may be controlled by the degree and duration of fluid-rock interaction, which is a function of the heat flux, crustal structure (faulting) and the permeability of the source rocks. Deposits at ultraslow ridges, including ultramafic-hosted deposits, are particularly enriched in gold. This is attributed to the higher permeability of the ultramafic source rocks achieved by serpentinisation and the inherent porosity of serpentine minerals, combined with relatively high gold concentrations in peridotite compared with mid-ocean ridge basalt. Variations in fluid chemistry, such as reducing conditions and the potential for increased sulphur availability at ultramafic-hosted sites, may also contribute to the high concentrations observed. Beehive chimneys, which offer more favourable conditions for gold precipitation, may be more prevalent at ultramafic-hosted sites due to diffuse low-velocity venting compared with more focussed venting at basalt-hosted sites.
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期刊：
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DOI：
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发表时间：
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期刊：
The Journal of Geology
影响因子：
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